It is generally known in the steel making industry to add aluminum to molten steel as a deoxidizer to remove oxygen from the molten steel. Oxygen may form bubbles or voids within the steel, which detrimentally affect its properties.
When casting an aluminum-killed molten steel, the added aluminum reacts with the oxygen present in the molten steel to produce non-metallic inclusions such as alumina. The aluminum-killed molten steel is typically cast by pouring the molten steel from a conventional ladle into a tundish. A pouring nozzle is secured to the bottom wall of the tundish and directs the molten steel into a mold therebelow. A known problem with aluminum-killed steel is that the .alpha. alumina tends to adhere and accumulate on the surface of the bore of the nozzle. This build-up of alumina on the surface of the bore restricts flow therethrough, thereby affecting production performance, as well as product quality.
Nozzles have been developed utilizing special refractory compositions along the surface of the nozzle bore. For example, calcium zirconate graphite refractories have been used to form the inner portion of the nozzle that forms the nozzle bore. This refractory material basically provides calcium oxide (contained in the calcium zirconate) to react with the a alumina to produce low-melting point compounds, such as CaO.Al.sub.2 O.sub.3 and 3CaO.Al.sub.2 O.sub.3. While calcium zirconate graphite nozzles have improved anti-clogging characteristics over conventional nozzles such as alumina graphite, only the calcium oxide near the surface of the bore tends to react with the .alpha. alumina, and once this surface calcium is depleted, the ability of the refractory to prevent adhesion and accumulation of additional a alumina diminishes. It has been known to add calcium silicate (CaO.SiO.sub.2) to the calcium zirconate graphite refractory to add additional calcium to the bore lining to facilitate the calcium oxide/alumina reaction. The calcium oxide contained in the calcium silicate basically provides calcium oxide to drive the calcium oxide/alumina reaction. The amount of calcium oxide in the calcium silicate, however, is important in that any calcium oxide that is not dissolved in the form of a solid-solution into calcium silicate, may react violently with water or moisture in the air to deteriorate the structure of the nozzle.
It is therefore highly desirable to add additional calcium oxide to a calcium zirconate graphite nozzle in a form which is resistant to water and moisture in the air, yet will provide the necessary calcium oxide in the presence of molten, aluminum-killed steel to drive the calcium oxide/alumina reaction.
The present invention provides a refractory material for forming the bore of a molten steel pouring nozzle, which refractory is less susceptible to water or moisture, yet provides additional calcium oxide to prevent adherence of alumina impurities on the bore of the pouring nozzle.